Tuned oscillatory circuits



Jan. 16, 71934. c. J. FRANKS TUNED OSGILLATORY CIRCUITS Filed D60. 28, 1931 yj f f Patented Jan. 16, 1934 TUNED OSCILLATORY cmcUrrs Christopher J. Franks, Boonton, N. 1., assignor to Radio Frequency Laboratories, Incorporated, Boonton, N. J., a corporation of New Jersey Application December 28, 1931 Serial No. 583,491

24 Claims.

This invention relates to tuned oscillatory cirthe oscillator circuit includes a large lagging condenser in series with the tuning condenser,

and a small condenser shunted across the tuning condenser to increase its residual or minimum '20 capacity above that of similar condenser sections that tune the carrier frequency stages. The

values of these series and shunt capacities will be different for different frequency ranges and it is therefore impossible to adjust the oscillator 25 for a plurality of frequency bands by the simple expedient of changing only the oscillator inductance.

An object of the invention is to provide a simple and eflicient multi-range oscillator circuit in which the frequency bandcovered by the oscillator may be changed by switching impedances into and out of the oscillator network. A further object is to provide a multi-range vacuum tube oscillator in which inductances of different effective values are included in the oscillatory circuit to change the tuning range, one of the inductances being a permanent part of the tube circuits and serving as the coupling between the oscillatory circuit and the tube for all tuning ranges.

More particularly, an object is to provide a vacuum tube oscillator having, in series with the tuning condenser, an inductance and two series capacities, and in which either a high frequency inductance or a small condenser may be con-.

nected between the junction of the series capacities and the junction of the tuning condenser and the first inductance.

These and other objects of the invention will be apparent from the following specification when taken with the accompanying drawing in which the single view is a fragmentary circuit /diagram of a suprheterodyne receiver including a double-range oscillator embodying the invention.

In the drawing, the reference numerals 1, 2 identify, respectively, a carrier wave amplifier tube and first detector of a superheterodyne receiver. The input circuits of these stages include similar inductances L and tuning condensers C, appropriate provision being made for adjusting the magnitude of the inductances L to two different values to effect tuning over two different frequency bands. So far as concerns the present invention-it is immaterial whether the inductance coils be changed or, as illustrated, portions of the low frequency coils L be short-circuited by switches 3 to adjust the receiver for the reception of higher frequencies. As illustrated, the switches 3 are closed and the carrier frequency stages are therefore adjusted for reception of signals in the higher frequency band.

In the novel oscillator circuit, the plate induct-. ance 5 is coupled to a grid coil 6; a third coil '7 being coupled to coil 6 and included in the cathode circuit of the detector 2 for impressing the local oscillations upon the first detector.

Two condenses 8, 9 are connected in series with each other between the high potential ends 30 of the grid coil 6 and the tuning condenser C which, as indicated by broken lines 10, is one section of a gang condenser employed for simultaneously tuning the oscillator and the carrier frequency stages. An inductance 11 and small 35 condenser 12 are arranged for alternative connection between the joined low potential terminals of the grid inductance 6 and oscillator tuning condenser C, and the junction of condensers 8 and 9 by means of a double throw switch 13. A second small condenser 14 is shunted across the oscillator condenser C. As indicated on the drawing, the condensers 8, 9, 12 and 14 are adjustable to effect alinement of the oscillator with the carrier frequency stages but, once adjusted, are not varied for the reception of signals in either frequency band.

For reception in the higher frequency band, the oscillator switch 13 is positioned, as shown, to include the inductance 11 in the impedence network. The oscillatory circuit of tube 4 is then constituted by the inductance 11, the high frequency lagging condenser 9, and the tuning condenser C in shunt with the condenser 14. The values of condensers 9 and 14 are adjusted, in accordance with known practice, to provide a constant frequency difference between the oscillator frequency and the resonant frequency of the carrier wave stages as the gang condenser is adjusted. It is to be noted that the inductance 6 is not included in this high frequency oscillator circuit but serves as a coupling between the oscillatory circuit and the tube.

Consideration of the characteristics of a circuit of this type will show that, to maintain the predetermined frequency difference as the carrier wave stages are changed to a lower frequency band, the inductance of the oscillator circuit must be increased, a lower series laggingv capacity is required and the tuning condenser must have a higher residual or bottom capacity.

Each of these conditions obtains when the switch 13 is moved to its alternative position to include condensers 12 in the tube circuits and to exclude inductance 11. The grid coil 6 now constitutes the inductance of the oscillatory circuit, the lagging capacity is provided by the serially connected condensers 8, 9 and is therefore less than the lagging capacity 9 of the high frequency circuit. At the same time, the condenser 12 is effectively shunted across the oscillator tuning condenser C to increase its residual capacity. By adjustment of condensers 8 and 12, the low frequency tuning of theoscillator may be made to follow, with the desired frequency difference, the tuning of the carrier wave stages over their low frequency range. This adjustment does not require any change in the previously determined values of the condensers of the high frequency oscillatory circuit.

The tube will oscillate freely over both frequency bands and the elements of each oscillatory circuit may be selected or adjusted for correct operation over its particular fequency band.

I claim:

1. A vacuum tube system adapted for operation in more than one band of frequencies, comtaneously with the said variable reactive circuit element of one sign connected to said tube, a relatively fixed and a variable reactive circuit element both of opposite sign to said first reactive circuit element and means for alternatively completing for said vacuum tube either a periodic output circuit including said first circuit element and said variable circuit element or a periodic output circuit including said variable circuit element and having an inductance and a capacitance which differ from the corresponding values of said periodic circuit for any given position of said variable cirucit element.

2. The invention as set forth in. claim 1, wherein the eifective periodic output circuit of said tube is coupled to an external circuit which includes a variable reactive circuit element mechanically connected to and adjustable simultaneously with the said variable reactive circuit element included in the output circuit of said tube.

3. A vacuum tube system adapted for operation in more than one band of frequencies, comprising a vacuum tube connected to an inductance, a reactive network connected to said inductance and including in series a tuning condenser and capacitance, and means for alternatively completing either a tunable oscillatory circuit including said inductance and tuning on-denser or a second tunable oscillatory circuit including said tuning condenser and having an inductance and a capacitance differing from the corresponding values of said first oscillatory circuit for any given position of adjustment of said tuning condenser.

4. In a transmission system, the combination with a first circuit tunable over a plurality of frequency bands by a section of a gang condenser, of an oscillatory circuit adapted for operation in substantially the same frequency bands as said first circuit, said oscillatory circuit being tuned throughout each of said hands by a second section of said gang condenser and including a band-changing switch, a plurality of fixed inductances, a plurality of fixed condensers, and circuit connections whereby in each band determined by the position of said switch both the effective inductance and the effective capacitance are different from the corresponding values for every other band at any given position of adjustment of said tuning condensers.

5. In a transmission system, the combination with a pair of approximately identical tuned circuits, including substantially identical reactive circuit elements ganged for simultaneous adjustment for tuning, and only one of said circuits including lagging reactive circuit element to maintain a constant frequency difference between the resonant frequencies of said circuits for all adjustments of said ganged circuit elements, of switch meansfor shifting the tuning ranges of each circuit and for simultaneously changing the magnitude of the lagging circuit element to such new magnitude that the circuits exhibit the same constant frequency difference when tuned over their respective changed tuning ranges by adjustment of said ganged circuit elements.

6. In a transmission system, the combination with a vacuum tube; and a network coupled to said tube and including in series, a plurality of fixed circuit elements providing reactances of opposite types and an adjustable circuit element having a reactance of but one type of relatively fixed means operative without disturbing the connections of said serially connected circuit elements for simultaneously changing both the effective magnitudes, for any adjustment of said adjustable circuit element, of both types of said fixed circuit elements in the oscillatory circuit which includes said tuning reactance; said means comprising a relatively fixed reactive circuit element, and switch means for alternatively including the same in or excluding the same from said network.

7. The invention as set forth in claim 6, wherein said magnitude changing means includes a pair of relatively fixed reactive circuit elements of opposite type, and switch means for alternatively including either of said pair of circuit elements in said network.

8. A transmission system of the type including two circuits which may be simultaneously tuned over approximately identical frequency bands by the changes in the magnitude of substantially identical tuning circuit elements of one type 01 reactance included in each of the said circuits, each circuit including a fixed circuit element being reactance of the opposite type, and only the second of said circuits including a relatively fixed lagging circuit element having reactance of the first type to establish a constant frequency difference between the resonant frequencies of said circuits, characterized by the fact that each circuit includes means for changing the effective magnitude of its reactive circuit element of the second type to change the frequency range over which it may be tuned. and said second circuit includes means for changing the magnitude of said lagging circuit element simultaneously with the changes in the magnitude of its reactance of the second type.

9. In a transmission system including two variably tuned circuits each tuned over one frequency band by a continuously variable section of a, unitary tuning control, a lagging reactive circuit element in one of said circuits for maintaining throughout said frequency band a substantially constant difference between the resonant frequencies of said circuits, means for stepwise alteration of a relatively fixed reactive circuit element in each of said circuits to permit the operation of both circuits over a second frequency band, and means for simultaneous stepwise alteration of said lagging reactive circuit element to permit the establishment of a constant frequency difference throughout the second of said bands which is substantially equal to the frequency difference maintained throughout the first of said bands.

10. A superheterodyne receiver comprising a carrier frequency circuit and an oscillator, both. tuned by a unitary tuning control, a relatively fixed lagging reactive circuit element in the circuit of said oscillator whereby a constant difference is'maintained between the frequency of said oscillator and the resonant frequency of said carrier circuit, switch means for shifting the tuning range of said carrier circuit from one band of frequencies to another band, and switch means for shifting the tuning range of said oscillator circuit from one band of frequencies to another and for simultaneously changing the magnitude of said lagging reactive circuit element.

11. In an oscillatory network adapted to be tuned over two frequency bands, the combination with two main impedance elements comprising an inductance and a tuning condenser, and a plurality of relatively fixed condensers connected in series with each other and with said main tuning elements to form a main circuit, of an impedance path connected across said main circuit to provide two branches which each include a relatively fixed condenser and one of said main impedances; said path including an inductance, a relatively fixed condenser, and switch means for alternatively including either the inductance or the condenser of said path in the circuit of said network.

12. In an oscillator adapted to be tuned over two frequency bands, the combination with a tube having a cathode, grid and anode elements; an inductance included in a circuit between two elements of said tube; of a tuning condenser, and capacitive impedance cooperating with said tuning condenser and inductance to constitute an oscillatory circuit, a second inductance of lowermagnitude than said first inductance, and switch means for connecting said second inductance in circuit with said tuning condenser and a portion of said capacitive impedance to constitute an oscillatory circuit having a different inductance, a higher maximum, and a lower minimum capacity than said first oscillatory circuit.

13. In an oscillator adapted to be tuned over two frequency bands by an adjustable condenser, the combination with a vacuum tube having grid and plate inductances, a tuning condenser, and circuit elements including series capacitive impedance cooperating with said grid inductance and said tuning condenser to form a first oscillatory circuit, of a third inductance and switch means for shunting said third inductance across said first oscillatory circuit to form a new oscillatory circuit tunable by said tuning condenser over a higher frequency band than said first oscillatory circuit, the total series capacitance of said new oscillatory circuit being higher than that of said first circuit for any given setting of said tuning condenser.

14. In an oscillator, the combination with a vacuum tube and an inductance effectively included in a,circult of said tube, a circuit connected across said inductance and including a tuning condenser, and a relatively fixed condenser effectively in parallel with said inductance and with said tuning condenser, whereby the said inductance constitutes the inductive reactance of the oscillatory circuit which determines the frequency of oscillatory currents generated by said tube; of means for alternatively effecting operation over a higher frequency band, said means including an inductance and means for substituting said second inductance for said relatively fixed condenser as an operative element effectively in parallel with said first inductance and with said tuning condenser.

15. In an oscillatory circuit adapted to be tuned over a plurality of frequency bands, an oscillatory network including an inductance, a circuit shunted across said inductance and including, in series, a tuning condenser and two relatively fixed condensers, and a path shunted across said tuning condenser and one of said fixed condensers, said path alternatively including an inductive or a capacitive reactance, thereby to determine the frequency band over which the circuit may be tuned.

16. In a superheterodyne receiver, a first detector operating into a fixed intermediate frequency amplifier, an input circuit for said detector including one of a plurality of substantially identical sections of a gang condenser and alternatively inductances of two magnitudes, whereby said detector input circuit may be tuned over two frequency bands, an oscillator tube, and

an oscillatory network adapted to resonate throughout the tuning range of said gang condenser at frequencies which differ from the corresponding resonant frequency of said detector input circuit by a constant frequency difference equal to a fixed intermediate frequency, said network including a second section of said gang condenser, relatively fixed capacitance, and

switch means for placing relatively fixed capacitance of different values for each frequency band effectively in series with said second sec-' tion of said gang condenser.

17. The invention as set forth in claim 16, wherein the oscillatory circuit established during the reception of signals in the higher of said frequency bands has a higher maximum capacity and a lower minimum capacity than the oscillatory circuit established by said switch means for reception of signals in the lower frequency band.

- 18. In a receiver having a carrier wave trans mission stage including inductances of two values to permit the tuning of said stage to resonance over two frequency bands, an oscillator comprising a vacuum tube, an inductance effectively included in a circuit of said tube, a plurality of relatively fixed condensers and a tuning condenser in series with each other and with said inductance to constitute an oscillatory circuit, a' shunt path across said oscillatory circuit, said path including switch means and alternatively either a capacitance or an inductance whereby said first inductance serves, when said shunt path includes said second inductance, as a coupling between said tube and the oscillatory circuit which includes said second inductance and said tuning condenser.

19. In a superheterodyne receiver, the combination with a carrier wave transmission stage, and means for tuning said stage over two frequency bands by one of a plurality of substantially identical sections of a gang condenser, of a vacuum tube, and an impedance network coupled to said tube to constitute therewith a generator of oscillatory currents for beating with received signal energy, said network including a second section of said gang condenser, a pair of inductances of different magnitudes, a plurality of relatively fixed condensers, and switch means for alternatively connecting either of said inductances in circuit with said second condenser section and at least one of said relatively fixed condensers, thereby to form either one or two oscillatory circuits tunable by said condenser section.

20. In a receiver including means for adapting the same to receive signals within two difierent frequency bands, a double-range oscillator comprising the combination with a vacuum tube having a cathode, grid and anode, of an inductance between grid and cathode, capacitive impedance in shunt with said inductance, and comprising, in series, two relatively fixed condensers and a tuning condenser, a third relative 1y fixed condenser, a second inductance, and switch means for alternatively connecting either said third condenser or said second inductance in shunt with said tuning condenser and one of said two relatively fixed condensers in series therewith.

21. The invention as set forth in claim 20, wherein the tuning condenser of said oscillator comprises one of a plurality of sections of a gang condenser employed for tuning said receiver to resonance at the frequency of the desired signal.

22. In an oscillatory network. adapted to be tuned over two frequency bands, the combination with two main impedance elements comprising an inductance and a tuning condenser, and a plurality of relatively fixed condensers in series with each other and with said main tuning elements to comprise a main circuit, of an impedance path shunted across said main circuit to provide two branches which each include a relatively fixed condenser and one of said main impedances; said path including inductive reactance, capacitive reactance and switch means adjustable to alternative positions to make the effective impedance of said shunt path inductive or alternatively to make the effective impedance thereof capacitive.

23. In an oscillatory network adapted to be tuned over two frequency bands, the combination with two main impedance elements comprising an inductance and a tuning condenser, and a plurality of relatively fixed condensers in series with each other and with said main tuning elements to comprise a main circuit, of means adjustable at will to adapt said network for tuning over a higher or a lower frequency range, said means being shunted across said main circuit to divide the same into two branches which each include a relatively fixed condenser and one of said main impedances, and said means comprising reactances of opposite signs and a switch for making the effective reactance of said means capacitive to adapt said network for tuning over the lower frequency range and for making the effective reactance of said means inductive to adapt raid network for tuning over the higher frequency range.

24. In an oscillatory network adapted to be tuned over two frequency bands, the combination with two main impedance elements comprising an inductance and a tuning condenser, and a plurality of relatively fixed condensers in series with each other and with said main tuning elements to comprise a. main circuit, of an im pedance path shunted across said main circuit to provide two branches which each include a relatively fixed condenser and one of said main impedances; said path including inductive reactance, capacitive reactance and switch means adjustable to one position to exclude said capacitive reactance from said shunt path to adapt said network for tuning over a higher frequency range and alternatively adjustable to another position to make the effective impedance of said shunt path substantially equal to said capacitive impedance to adapt said networkfor tuning over a lower frequency band.

CHRISTOPHER J. FRANKS.

the oscillatory circuit which includes said second inductance and said tuning condenser.

19. In a superheterodyne receiver, the combination with a carrier wave transmission stage, and means for tuning said stage over two frequency bands by one of a plurality of substantially identical sections of a gang condenser, of a vacuum tube, and an impedance network coupled to said tube to constitute therewith a generator of oscillatory currents for beating with received signal energy, said network including a second section of said gang condenser, a pair of inductances of different magnitudes, a plurality of relatively fixed condensers, and switch means for alternatively connecting either of said inductances in circuit with said second condenser section and at least one of said relatively fixed condensers, thereby to form either one or two oscillatory circuits tunable by said condenser section.

20. In a receiver including means for adapting the same to receive signals within two different frequency bands, a double-range oscillator comprising the combination with a vacuum tube having a cathode, grid and anode, of an inductance between grid and cathode, capacitive impedance in shunt with said inductance, and comprising, in series, two relatively fixed condensers and a tuning condenser, a third relatively fixed condenser, a second inductance, and switch means for alternatively connecting either said third condenser or said second inductance in shunt with said tuning condenser and one of said two relatively fixed condensers in series therewith.

21. The invention as set forth in claim 20, wherein the tuning condenser of said oscillator comprises one of a plurality of sections of a gang condenser employed for tuning said receiver to resonance at the frequency of the desired signal.

22. In an oscillatory network adapted to be tuned over two frequency bands, the combination with two main impedance elements comprising an inductance and a tuning condenser, and a plurality of relatively fixed condensers in series with each other and with said main tuning elements to comprise a main circuit, of an impedance path shunted across said main circuit to provide two branches which each include a relatively fixed condenser and one of said main impedances; said path including inductive reactance, capacitive reactance and switch means adjustable to alternative positions to make the effective impedance of said shunt path inductive or alternatively to make the effective impedance thereof capacitive.

23. In an oscillatory network adapted to be tuned over two frequency bands, the combination with two main impedance elements com prising an inductance and a tuning condenser, and a plurality of relatively fixed condensers in series with each other and with said main tuning elements to comprise a main circuit, of means adjustable at will to adapt said network for tuning over a higher or a lower frequency range, said means being shunted across said main circuit to divide the same into two branches which each include a relatively fixed condenser and one of said main impedances, and said means comprising reactances of opposite signs and a switch for making the eilective reactance of said means capacitive to adapt said network for tuning over the lower frequency range and for making the effective reactance of said means inductive to adapt raid network for tuning over the higher frequency range.

24. In an oscillatory network adapted to be tuned over two frequency bands, the combination with two main impedance elements comprising an inductance and a tuning condenser, and a plurality of relatively fixed condensers in series with each other and with said main tuning elements to comprise a main circuit, of an impedance path shunted across said main circuit to provide two branches which each include a relatively fixed condenser and one of said main impedances; raid path including inductive reactance, capacitive reactance and switch means adjustable to one position to exclude said capacitive reactance from said shunt path to adapt said network for tuning over a higher frequency range and alternatively adjustable to another position to make the effective impedance of said shunt path substantially equal to said capacitive impedance to adapt said network for tuning over a lower frequency band.

CHRISTOPHER J FRANKS.

CERTIFICATE or comuzcriou.

Patent No. l, 943, 790.

January 16, 1934.

CHRISTOPHER J. FRANKS.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Page 2, line '39, claim I, strike out the syllable and words "taneously with the said variable" and insert instead prising a vacuum tube, a first; and line 50, before "periodic" insert the word first; line 68, claim 3, for "on-denser" read condenser; line 119, claim 6, for "tuning reactance" read adjustable circuit element; and line 150, claim 8, for "reactance read reactive circuit element; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 20th day of March, A. D. 1934.

F. M. Hopkins 

